Auto rack rail road cars are used to transport automobiles. Most often, although not always, they are used to transport finished automobiles from a factory to a distribution center. A long standing concern has been the frequency of damage claims arising from high accelerations imposed on the lading during train operation. Many of these damage claims are related to slack action in the train. In this context, slack action includes (a) the free slack in the couplers; and (b) the travel of the draft gear of successive rail road cars under the varying buff and draft loads. Slack run-out occurs, for example, as a train climbs a long upgrade, and all of the slack is taken out of the couplings as the train stretches. Once the train clears the crest, and begins a relatively steep descent, the rail road cars at the end of the train may tend to accelerate downhill into the cars in front, closing up the slack. This slack run-in and run-out can result in significant longitudinal accelerations. These accelerations are transmitted to the automobiles carried in the auto-rack cars.
Historically, the need for slack was related, at least in part, to the difficulty of using a steam locomotive to “lift” (that is, move from a standing start) a long string of cars with journal bearings, particularly in cold weather. Steam engines were reciprocating piston engines whose output torque at the drive wheels varied as a function of crank angle. By contrast, presently operating diesel-electric locomotives are capable of producing high tractive effort from a standing start, without concern about crank angle or wheel angle. For practical purposes, presently available diesel-electric locomotives are capable of lifting a unit train of one type of cars having little or no slack.
Switching is another process having a long history. Two common types of switching are “flat switching” and “humping”. Humping involves running freight cars successively over a raised portion of track, and then allowing the car to run down-hill under gravity along various leads and sidings to couple with other cars as a train consist is assembled. For this type of operation the coupling speeds can be excessive, resulting in similarly excessive car body accelerations. For many types of rail road car, humping is now forbidden due to the probability of damaging the lading. An alternate form of switching is “flat switching” in which a locomotive is used to give a push to a rail road car, and then to send it rolling under its own inertia down a chosen siding to couple with another car. Particularly when done at night, the desirability of making sure that a good coupling is made tends to encourage rail yard personnel to make sure that the rail road cars are given an extra generous push. This often less than gentle habit tends to lead to rather high impact loads during coupling at impacts in the 5 m.p.h. (or higher) range. Forces can be particularly severe when there is an impact between a low density lading rail road car, such as an auto rack car, and a high density lading car (or string of cars) such as coal or grain cars.
Given this history, rail road car draft gear are designed to cope with slack run-out and slack run-in during train operation, and also to cope with the impact as cars are coupled together. Historically, common types of draft gear, such as that complying with, for example, AAR specification M-901-G, have been rated to withstand an impact at 5 m.p.h. (8 km/h) at a coupler force of 500,000 lbs. (roughly 2.2×106 N). Typically, these draft gear have a travel of 2¾ to 3¼ inches in buff before reaching the 500,000 lbs. load, and before “going solid”. The term “going solid” refers to the point at which the draft gear exhibits a steep increase in resistance to further displacement. If the impact is large enough to make the draft gear “go solid” then the force transmitted, and the corresponding acceleration imposed on the lading, increases sharply. While this may be acceptable for coal or grain, it is undesirably severe for more sensitive lading, such as automobiles or auto parts, paper, and other consumer goods such as household appliances.
Consequently, from the relatively early days of the automobile industry, there has been a history of development of longer travel draft gear to provide lading protection for relatively high value, low density lading, in particular automobiles and auto parts, but also farm machinery, or tractors, or highway trailers. Draft gear development has tended to be directed toward providing longer travel on impact to reduce the peak acceleration. In the development of sliding sills, and latterly, hydraulic end of car cushioning (EOCC) units, the same impact is accommodated over 10, 15, or 18 inches of travel. As a result, for example, by the end of the 1960's nearly all auto rack cars, and other types of special freight cars had EOCC units. Further, of the approximately 45,000 auto-rack cars in service in 1997, virtually all were equipped with end of car cushioning units. A discussion of the developments of couplers, draft gear and EOCC equipment is given the 1997 Car and Locomotive Cyclopedia (Simmons-Boardman Books, Inc., Omaha, 1997 ISBN 0-911382-20-8) at pp. 640-702. In summary, there has been a long development of long travel draft gear equipment to protect relatively fragile lading from end impact loads.
In light of the foregoing, it is counter-intuitive to employ short-travel, or ultra short travel, draft gear for carrying wheeled vehicles. However, by eliminating, or reducing, the accumulation of slack, the use of short travel buff gear may tend to reduce the relative longitudinal motion between adjacent rail road cars, and may tend to reduce the associated velocity differentials and accelerations between cars. The use of short travel, or ultra-short travel, buff gear also has the advantage of eliminating the need for relatively expensive, and relatively complicated EOCC units, and the fittings required to accommodate them. This may tend to permit savings both at the time of manufacture, and savings in maintenance during service.
Further, as noted above, given the availability of locomotives that develop continuous high torque from a standing start, it is possible to re-examine the issue of slack action from basic principles. The use of vehicle carrying rail road cars in unit trains that will not be subject to operation with other types of freight cars, that will not be subject to flat switching, and that may not be subject to switching at all when loaded, provides an opportunity to adopt a short travel, reduced slack coupling system throughout the train. The conventional approach has been to adopt end of car equipment with sufficient travel to cope with existing slack accumulation between cars. In doing so, the long travel end of car equipment has tended to add to the range of slack action in the train that is to be accommodated by the draft gear along the train. The opposite approach, as adopted herein, is to avoid a large accumulation of slack in the first place. If a large amount of slack is not allowed to build up along the train, then the need for long-travel draft gear and other end of car equipment is also reduced, or, preferably, eliminated.
One way to reduce slack action is to use fewer couplings. To that end, since articulated connectors are slackless, use of articulated rail road cars significantly reduces the slack action in the train. Some releasable couplings are still necessary, to permit the composition of a train to change, if desired. Further, it is necessary to be able to change out a car for repair or maintenance when required.
To reduce overall slack, it would be advantageous to adopt a reduced slack, or slackless, coupler, (as compared to AAR Type E). Although reduced slack AAR Type F couplers have been known since the 1950's, and slackless “tightlock” AAR Type H couplers became an adopted standard type on passenger equipment in 1947, AAR Type E couplers are still predominant. AAR Type H couplers are expensive, and are used for passenger cars, as were the alternate standard Type CS controlled slack couplers. According to the 1997 Cyclopedia, supra, at p. 647 “Although it was anticipated at one time that the F type coupler might replace the E as the standard freight car coupler, the additional cost of the coupler and its components, and of the car structure required to accommodate it, have led to its being used primarily for special applications”. One “special application” for F type couplers is in tank cars, another is in rotary dump coal cars.
The difference between the nominal ⅜″ slack of a Type F coupler and the nominal 25/32″ slack of a Type E coupler may seem small in the context of EOCC equipped cars having 10, 15 or 18 inches of travel. By contrast, that difference, 13/32″, seems proportionately larger when viewed in the context of the approximately 11/16″ buff compression (at 700,000 lbs.) of Mini-BuffGear. It should be noted that there are many different styles of Type E and Type F couplers, whether short or long shank, whether having upper or lower shelves, as described in the Cyclopedia, supra. There is a Type E/F having a Type E coupler head and a Type F shank. There is a Type E50ARE knuckle which reduces slack from 25/32″ to 20/32″. Type F herein is intended to include all variants of the Type F series, and Type E herein is intended to include all variants of the Type E series having 20/32″ of slack or more.
Another way to reduce slack action in the draft gear is to employ stiffer draft gear. Short travel draft gear are presently available. As noted above, most M-901-G draft gear have an official rating travel of 2¾″ to 3¼″ under a buff load of 500,000 lbs. Mini-BuffGear, as produced by Miner Enterprises Inc., of 1200 State Street, Geneva Ill., appears to have a displacement of less than 0.7 inches at a buff load of over 700,000 lbs., and a dynamic load capacity of 1.25 million pounds at 1 inch travel. This is nearly an order of magnitude more stiff than some M-901-G draft gear. Miner indicates that this “special BuffGear gives drawbar equipped rail cars and trains improved lading protection and train handling”, and further, “The resilience of the Mini-BuffGear reduces the tendency of the draw bar to bind while negotiating curves. At the same time, the Mini-BuffGear retains a high pre-load to reduce slack action. Elimination of slack between coupler heads, plus Mini-Buff Gear's high pre-load and limited travel, provide ultralow slack coupling for multiple-unit well cars and drawbar connected groups of unit train coal cars.” Notably, unlike vehicle carrying rail cars, coal is unlikely to be damaged by the use of short travel draft gear.
In addition to M-901-G draft gear, and Mini-BuffGear, it is also possible to obtain draft gear having less than 1¾ inches of deflection at 400,000 lbs., one type having about 1.6 inches of deflection at 400,000 lbs. This is a significant difference from most M-901-G draft gear.
As noted above, auto rack rail road cars are end loaded. In circus loading, the vehicles are driven onto the rail road cars from one end. Each vehicle can be loaded in sequence by driving, or backing, along the decks of the rail road car units. The gaps between successive rail car units are spanned by bridge plates that permit vehicles to be driven from one rail car unit to the next. Although circus loading is common for a string of cars, end-loading can be used for individual rail car units, or multiple unit rail road cars, as may be.
From time to time some rail road cars are disconnected, and others are joined to the train. Traditionally, a pair of cars to be joined at a coupler are each equipped with one bridge plate permanently mounted on a hinged connection on one side of the car, typically the left hand side. In this arrangement the axis of the hinge is horizontal and transverse to the longitudinal centerline of the rail car.
In existing cars of this type, the bridge plate of each car at the respective coupled end is lowered, like a draw bridge, into a generally horizontal arrangement to mate with the adjoining car to permit loading and unloading. Each plate provides one side of the path so that the co-operative effect of the two plates is to provide a pair of tracks along which a vehicle can roll. When loading is complete, the bridge plates are pivoted about their hinges to a generally vertical, or raised, position, and locked in place so that they cannot fall back down accidentally.
It would be advantageous to have a bridge plate that can be moved to a storage, or stowed, position, with less lifting. A rail road car may sometimes be an internal car, with its bridge plates extended to neighbouring cars, and at other times the rail road car may be an “end” car at which the unit train is either (a) split for loading and unloading; (b) coupled to the locomotive; or (c) coupled to another type of rail road car. In each case, the bridge plate at the split does not need to be in an extended “drive-over” position, and should be in a stowed position. Therefore it is advantageous to have a rail car with bridge plates that can remain in position during operation as an internal car in a unit train, and that can also be stowed as necessary when the car is placed in an end or split position.